Field of the Invention
The present invention relates to a system for predicting occurrence of defective images which analyzes image data and predicts occurrence of a density irregularity specific to an image forming apparatus in regard to images formed by the image forming apparatus based on the image data, and relates to a program for predicting occurrence of the defective images.
Description of the Related Art
When an image is output by an image forming apparatus, there is a possibility that a density irregularity specific to the image forming apparatus occurs. An example of the specific density irregularity is a “firefly” which occurs circularly and is attributed to carrier particles of toner. Another example is a development-cyclic density irregularity which occurs in a belt-like shape and is attributed to deflection of a developing sleeve in a developing unit.
A level of each density irregularity depends on durability of the device or on environment and is constantly variable. In general, note that the level of each density irregularity varies extremely slowly and is almost uniform during continuous operation of the device.
When an image is printed by the image forming apparatus in which such a density irregularity occurs, the irregularity may be conspicuous or inconspicuous depending on a feature of an input image.
In a case where an image having a conspicuous density irregularity is printed, the image should be inspected and excluded by a detection device or operator as a defective image.
The inventions disclosed in JP 10-56570 A and JP 63-137251 A analyze image data in advance and then correct conditions of image forming processing.
The invention disclosed in JP 2012-39424 A reads out images from printouts and then carries out inspection processing. Herein, a speed of transmitting the printouts during readout is changed in accordance with inspection items.
The inventions disclosed in JP 10-56570 A and JP 63-137251 A satisfactorily adjust a feature of a gradient in accordance with image data so as to diminish defects in the gradient. However, those inventions do not include a unit for determining whether a density irregularity specific to an image forming apparatus is conspicuous to a human eye. Even though an image is printed with satisfactory gradient expression, there is a possibility that the density irregularity specific to the image forming apparatus occurs. Particularly because the image is printed with the satisfactory gradient expression, there is a possibility that the density irregularity specific to the image forming apparatus is conspicuous. Therefore, a problem of the density irregularity specific to the image forming apparatus may not be solved by the inventions disclosed in JP 10-56570 A and JP 63-137251 A.
In a case where the density irregularity is manually inspected, it is difficult to print and inspect simultaneously. Therefore, one hundred percent inspection is often carried out, which requires numerous man-hours. Accordingly, there is a demand on reducing printed materials to be inspected to a minimum.
A device for detecting printed materials disclosed in JP 2012-39424 A does not include a unit for predicting occurrence of defective images based on draft-image data of the printed materials. Therefore, such a device has no information for predicting on which printed material based on which draft-image data the defective images easily occur. Accordingly, there is no choice but to carry out one hundred percent inspection.
The device for detecting the printed materials disclosed in JP 2012-39424 A should properly set a threshold of the density irregularity for determining whether each image is the defective image. Otherwise, images having an inconspicuous density irregularity are determined as defective images, which leads to discarding the printed materials wastefully, or conversely, images having a conspicuous density irregularity are determined as non-defective images, which leads to shipping defective materials. Accordingly, there is a problem in accuracy of differentiating the non-defective materials from defective materials.